19.1 New products- Rexil: in the universe of wood

20/07/09

Rexil is a consolidant conceived for the preservation of wood artifacts of great value, and responds to stability and high penetration requisites. It is based on the aliphatic resin Regalrez 1126, a polymer derived from saturated hydrocarbons [1] and characterized by a low molecular weight. Its high stability to the ageing process has been tested and certified by accurate investigation [2,3].
In order to achieve the best level of impregnation in the artifact, Regalrez 1126 is dissolved (at the concentration of 25%) in White Spirit D40, a non-polar dearomatized solvent, without benzene, toluene and xylene. The use of an inert solvent makes the product perfectly suitable for treating polychrome art works. Furthermore, for the solution with the resin at 25%, the total viscosity is still low because the molecular weight is low (1250 uma). Anyway that viscosity may be more lowered by using the recommended ratio of 1:1, i.e. at the concentration 12.5%.
Low viscosity is necessary to deeply penetrate the texture of the wood artwork and makes this product more effective than longer chains based solvents like Paraloid B-27 and other acrylic resins. Rexil represents a valid option besides popular acrylic resins based consolidants. 
Rexil is outstanding in terms of stability and reversibility.
  
Below you can find the report on FTIR spectra, derived from different time of exposure under high level of UV radiations [2].

Effects on consolidation

Besides the well known case study on Regalrez 1126 carried out by Opificio delle Pietre Dure [4], we should mention the accurate research 
done by the researchers of the University of Calabria [5]. 
They tested two species of wood, commonly used in art handicrafts: poplar and fir woods. 
They applied Regalrez 1126 and Paraloid B-72, first one by one and then in sequence (both on the same sample).

TQ          
not treated
R            treated with Regalrez 1126 (at 10%) in butyl-acetate
P            treated with Paraloid B-72 (at 10%) in butyl-acetate
P+R        treated with Regalrez 1126 ( at 5%) and Paraloid B-72 at (10% )in butyl-acetate


The samples were aged through two methods:
  • UV exposure for 1000 hrs
  • freezing /defrosting 4 cycles, (dipping in water bath at t -5°C for 72hrs, warming at 60°C for 72hrs)
At the end of the ageing process physical and chemical properties have been measured (porosity, color...) and compared to the situation at the beginning of the experiment.

Porosity
: Regalrez is the product that less interferes with the substrate, whereas Paraloid (and when used in combination as well) is responsible for relevant alterations. By the way, more alterations were detected on the poplar wood. Regalrez 1126, because of its shorter chains (the molecular weight approaches 1000 uma, whereas for Paraloid M.w. ~70'000 uma) can penetrate the parenchymatic channels of the cell walls, while Paraloid goes into the lumen of the woody cells and reduces the porosity. The table below shows the porosity of the blank samples (TQ) vs. the treated ones. As reported, Regalrez does not significantly alter them.

     
                          TQ         
R          P         R+P
Fir-wood             30         30        27          26
Poplar-wood       25         23        19          19


FTIR measures: the analysis of the FTIR spectrum peak of the functional group -OH before and after the ageing treatment clearly shows that Regalrez 1126, when used alone provides the highest protection against photo oxidation, even a little bit better than R+P treatment. Of course, the not treated samples are the weakest.

Color:
 The change of the color for the samples under treatment depends on the quantity of the natural resin inside the wood texture and is more affected by the interaction with Paraloid . So the change is more evident on the fir -wood because poplar contains a small amount of resins. Anyway we should point out that Regalrez, when used alone is a very good stabilizer.

Variation in size :
 The dimensions of the samples treated with Regalrez are more stable than the others. The blank samples show high level of warping.

Mechanical resistance:
 As already detected in the previous case study by Opificio delle Pietre Dure, Paraloid improves the resistance to crack. The double combined treatment is good as well.

Protection against microbiological attacksThe researchers of the University of Calabria evaluated also the effect of the consolidant as a barrier against the microbiological attacks [6]. They monitored the growth and propagation of white-rot fungi (that degrade both lignin and cellulose and produce strong oxidant which virtually “combust ” the framework into a white soft mass) and brown-rot fungi (that attack only the cellulose increasing the porosity and causing the wood to split along lines of weakness). According to their findings the effect of the consolidant as a barrier for this kind of decay is related to the wood species (the application of both the resins on poplar (for both seasoned and not seasoned samples) is fully satisfactory. When using the products alone on fir-wood (not seasoned samples), the barrier is not completely developed; it is fully effective on the fir seasoned samples instead. 
That study case gave us some useful clues: the consolidation by the mean of these synthetic resins prevents or reduces the growing of micro-organisms. 
For a full protection is necessary to add 5% of Biotin R to Rexil.
With regard to the woodworm control, it is recommended to mix Rexil with PER-XIL 10, and apply to the part just once.

Conclusions
Although Regalrez 1126 does not reach the standards of Paraloid B-72, it perfectly fits to the wood-artifacts that do not need high reinforcement and that require a consolidant stable and easy to be removed (no cross-linking as time passes) because of their artistic value. Here another useful treatment procedure is suggested: one application of Rexil 1:1 solution (that deeply penetrate the substrate) followed by an application of another product like Paraloid.

Back side (poplar) of a painting on wood deeply ruined [pic by Roberta Moggia]

References:
  1. McGlinchey C.W. “The industrial use and development of low molecular weight resins: an examination of new products of interest to the conservation field”; ICOM Committee for Conservation (1990), Vol.II, 563-567.
  2. Borgioli L.; Camaiti M.; “Stabilizzazione di polimeri per la verniciatura di dipinti”, Convegno “Colore e conservazione”, Thiene (2004)
  3. Talarico F. “Proprietà delle vernici idrocarburiche e prospettive”, Kermes 72, (2009), 70-73.
  4. Castelli G.; Gigli M.C.; Lalli C.; Lanterna G.; Weiss C.; Speranza L.; “Un composto organico sintetico per il consolidamento del legno: sperimentazione, misure e prime applicazioni” Bollettino OPD (2003).
  5. Crisci G.M., Cuscino M., La Russa M.F., Malagodi M., Ruffolo S.A., Russo S., Saccarello M.V.; “Caratterizzazione delle proprietà del Regalrez 1126 e del Paraloid B72 nel consolidamento del legno” Atti del VI Congresso Nazionale IGIIC, Spoleto (2008).
  6. Clausi M., Crisci G.M., La Russa M.F., Malagodi M., Palermo A.M., Ruffolo S. A.; “Studio degli effetti prodotti da funghi da carie bianca e bruna su legno trattato con prodotti consolidanti”, Convegno “Scienza e Beni Culturali” Bressanone (2009), 465-474.
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